Liquid rheostat



ET AL,

May 24, 192'?u LQUID RHEOSTAT Filed Jan, 5, 1925 Patented May Z4, 1927.

UNITED STATES PATENT OFFICE.

BERTRAM GRAY AND ROBBINS CURTIS, OF JOHANNESBURG, TRANSVAAL, SOUTH AFRICA.

"v LIQUID RI-IEOSTAT.

Application led January 5, 1925, Serial No. 625, and in Union of South Africa January 11, 1924.

The present invention has reference to liquid rheostats and more particularly those for controlling large multi-phase motors which are frequently started and stopped.

The invention provides a liquid rheostat capable of controlling heavy currents without danger of arcing, which offers a low resistance to the full speed current whilst avoiding liability to jam in the full speed position, and which affords the advantage over the usual closed-in liquid starter, that all its parts are open to view and those parts which are likely to require adjustment or repair are out of the electrolyte.

The invention also provides for the cooling of the electrolyte in a simple and inexpensive manner.

In the accompanying drawings Fig. I is a perspective view of a starter for a large three-phase hoist motor with the electrodes separated. v

Fig. II is an enlarged vertical section on a plane passing through a pair of the electrodes, showing them closed towards one another.

Rheostats of the kind in which the immersion of a series of parallel electrode-blades is varied have the disadvantage that with small immersione the cross sectional area of the liquid path becomes so reduced, without corresponding lengthening of the path, that there is danger of arcing.

The other usual kind in which the cross sectional area of the liquid path remains constant whilst its length is varied by movement of the electrodes towards and from one another requires a non-conducting or insulated container which is liable to break or otherwise become defective.

The present invention aims particularly to overcome these drawbacks by varying the length of a resistance path between parallel electrode surfaces inversely with itsv crosssectional area, said path being always substantially perpendicular to the electrode surfaces.

Referring to Figs. I and II of the drawings, the numeral 2 indicates three fixed electrodes, one for each phase. These fixed electrodes' are preferably also the insulated set. The other electrodes 3 of the pairs of electrodes are movable simultaneously in a defined path relatively to their fixed electrodes Q, being, in this example moved vern tically by being severally fixed to a common beam structure 4 which is raised and lowered by ropes 5 clamped to and passed around pulleys 6 coupled together by a coupling rod 7. The weight of the beam 4 and the electrodes 3 is balanced by a counterweight 8.

The electrodes of each pair provide conducting surfaces such as the pairs 9, 9, 10, l0ZL etc. which are parallel with one another and which are also substantially inclined to the direction of relative movement of the electrodes. A body of electrolyte is maintained between said pairs of surfaces. In the example under discussion the body of electrolyte is carried in the fixed electrode 2 which is constructed as a metallic container of downwardly tapering form. It is shown of pyramidal shape providing the conducting surfaces 9, 10, ll, l2; whilst the movable electrode is similarly of pyramidal shape providing the similar and parallel conducting faces 9, 10a, lla and 12a.

The liquid lying` between the pairs of surfaces 9, SPl etc. constitutes the resisting medium and the electrode 3 is immersed to a greater or less extent in the liquid for the purpose of introducing less or more resistance into the rotor circuit of the three-phase motor.

As the result of thus inclining the conducting surfaces to the direction of movement, the pairs such as 9, 9a remain parallel to one another while approaching or separating. Also by reason of their constant parallelism and of the variable immersion of the electrode 3, the current path is always substantially perpendicular to the inclined surfaces. IVhen therefore the immersion of the movable electrode is least, as in Fig. I, the electrode area through which the current passes is the minimum, whilst the surfaces are most widely separated. On the other hand, when the electrodes are close together as in Fig. II, the cross sectional area of the liquid path is a maximum. In either case, therefore, the danger of arcing is rendered negligible.

The pulleys 6 are operated from a hand wheel 13 by means of a shaft 14 on which said hand wheel is fixed, a. crank 15 in the shaft 14 and a connecting rod 16. The hoist motor being reversible and controlled as to direction by the direction in which the hand wheel 13 is turned, it is necessary that the movement of the electrodes 3 should be the ICU same whatever"theidircction of rotation of the wheel 13. The connecting rod 16 vis accordingly attached to its pulley at a radius greaterlthanfthe*radius of .the crank V15 so. that a full revolution of the latter causes the pulleys to oscillate through an arc of less than 180 degrees.

Provision is made for constantly bathing the electrode surfaces with electrolyte, and when one velectrode is a container as described, effective bathing is brought about by .passing a vstream of electrolyte into the container, so that4 .it llows between the opposite lelectrode surfaces. y

In the arrangement of Figs. I `Vand II, electrolyte is supplied by means of'an uninsulated Vmain pipe 17, from which depend three branch .'pipesil8, each controlled by asepara-te valve 18a. `The electrolyte is discharged through t-he open lower end 19 of each branchl` and passes through an opening y20 in the lower end'of the upper electrode 3, intothe lower electrode 2. The apex 21 of the electrode 2 is annularly cupped as shown to facilitate reversal of Vflow of the'electrolyte, whichpasses upwards between the electrode surfaces and'ovcrflows fromthe lip 22.

,The stream of'electrolyte, issuing asa jet .from the pipe 18 and .passing through the open lower end-fof 'the movable .electrode3,

v exerts anejector action on whatever electrolyteis contained within*saidelectrode, tending to 'lower the level of the same and ,preventing electrolyte from spilling over the top of themovable electrode 3 which would otherwise tend to occur when said electrode is suddenly .plunged intorthe electrolyte in 'the lower electrode 2er when the electrodes are closely approached to one another. The electrolyte overflows 'from the Llip 22 intofa sump 23 Yas a thin sheet; andunder vappropriate atmospheric conditions it is thereby cooled sutliciently 'to render any further cooling steps unnecessary. The electrolyte collected -in the sump 23 is returned to the ldistributing pipe 17 by the pump 24.

As mentioned above, the upper electrodes 3 are retained in their alinement with the Alower electrodes 2`bygravity; but to prevent their accidentally swinging, collars 25 are .provided which loosely encircle the pipes 1S so that the latter act as guides.

The alinement of the electrodes of a 'pair is provided for by making the bearers 26 `for the lower electrodesA adjustable in both horizontal directions on the insulators 27.

In order to'enable the electrodes cfa-pair to bebrought very closely together without touching, one or both of them maybe fitted 'with studs-28 (Fig. Il) of'non-conducting material such as rubber. y tact 'with the opposite electrode 'face .when 'the electrodes `are brought together, Acentre y'one electrode 'with'the other, and also space vthem apart so that 'a 'very `tlii'n 'electrolyte These make 'consheet isleft between Athem with consequent low resistance at'full load. The inclination of the electrode surfaces is such as to avoid their wedging with one another `When-'thus brought together.

If actual metallic contact at full speed is desiredethis may be effected systematically by means of spring contacts 29 on one of the electrode surfaces, which project so 'as to make contact with the surface of the other electrode, when the insulating studs 28 make Contact. n

The maintenance ofthe continuity of the circuit at lthe high resistance position, which is desirable in starters of 'the type in question, is effected in the example shown'by the-pipes 18projecting into the electrolyte inthe container-SI2, and alsoby dippers 30 'which extend from the electrodes 2 into the `electrolyteibetween'the upper parts of the sui-faces being considerably hotter than that 'between vtheir lower parts, the plates may in such cases be somewhat diverged Ifrom one 'another upwardlyso lengthening'the current path to compensate .for the greater conductivity of the heated electrolyte.

lVe claim: l A 1. A multipliase liquidlrheostat com rising .pairs of downwardly tapered electro( es, one

electrode of each pair being imperforate and constituting an open-'topped container lfor tno electrolyte andbeing also `'fixed andlins'ulated, the other electrode of each pair being uninsulated yand presenting an iinn pertorate external surface complementary to the internal surface of the container yelectrode and of'approximately the saine area, and "being lapertured at its point, means Jfor continuously feeding electrolyte lfrom arpoint distant from theinternal surface o'f'the conltainer electrode and so that it passes through the aperture at the .point of the internal electrode rand upwardly Abetween the at jacentsurfaces of the electrodes, and means for simultaneously moving the uninsulated-electrodcs to vary theiiwimlnersion in the electrolyte in the .container electrodes.

2. ln fa multiphase liquid rheostat, the

combination of downwardly Vtapered elec- Vtro'desforming containers Ifor the electrolyte,

said -containerlectrodes'being iixed and insulated,.a m',lpil'urahty of corresponding unins'ulz'rted lectrodes, -abeam to which the 'uninsulated 'electrodes fare attached, 'a lplu- 'r'alit'y of "rotatable pulleys, flexible -means supporting the beam and wound on said pulleys, and means for rotating the pulleys simultaneously whereby the beam is raised and lowered parallel with itself.

3. In a liquid rheostat, a hollow downwardly tapered electrode forming a container for the electrolyte, an electrode movable for immersion in the electrolyte in the container electrode, a pipe arranged to deliver a stream of electrolyte into the container electrode, the container electrode having an extended overflow lip such as to cause the electrolyte to fall from it in sheet form, a sump arranged below the container electrode and at such a distance that the electrolyte is substantially cooled in falling therein from the lip and a circulating pump drawing electrolyte from the sump and returning it to the delivery pipe.

4. In a multiple phase liquid rheostat, a fixed and insulated hollow electrode for each phase, adapted to contain a body of liquid and providing an overflow lip therefor, movable electrodes adapted to be inserted into the hollow electrodes, connected electrolyte supply pipes each arranged to deliver a stream of electrolyte towards a hollow electrode, the delivering ends of said pipes being within the hollow electrodes below the overflow lips thereof whereby they maintain electrical connection between the phases.

5. In a multiple phase liquid rheostat, a fixed hollow electrode foreach phase, a movable electrode adapted to be inserted into the fixed electrode, a main electrolyte supply pipe, branch pipes therefrom adapted to deliver a stream of electrolyte into each hollow electrode, and means for separately controlling the flow from the main pipe to each branch pipe.

6. In a liquid rheostat, a fixed hollow electrode adapted to contain a body of liquid, an electrode movable vertically for insertion into the hollow electrode, a vertical pipe adapted to deliver a stream of electrolyte towards the hollow electrode, said pipe forming a guide for the movable electrode.

7. In a liquid rheostat, a pair of hollow electrodes of downwardly tapered form and movable relatively to one another, one being adapted for insertion into the other, means to maintain a body of electrolyte within said electrodes, the inner electrode having an opening at its lower end, and means to deliver a. stream of electrolyte into the inner electrode and through said opening` whereby the stream entrains electrolyte within the inner electrode.

8. In a liquid rheostat, a hollow electrodo adapted to contain electrolyte, a hollow electrode movable for variable immersion in the electrolyte having an opening in its lower end, means to deliver electrolyte through said opening into the container electrode and means for facilitating reversal of the direction of flow, of the electrolyte issuing' from said opening.

9. In a liquid rheostat, a hollow electrode adapted to contain electrolyte, an electrode h movable for immersion in the hollow electrode, means for delivering a stream of electrolyte into the hollow electrode, the latter having an overflow for surplus electrolyte, and a sump arranged to collect electrolyte overflowing from the hollow electrode, said sump being at such a distance below the hollow electrode that the electrolyte is substantially cooled in falling from the hollow electrode to the sump.

10. In a liquid rheostat, a hollow electrode adapted te contain electrolyte, an electrode movable for immersion in the hollow electrode and means for delivering` a stream of electrolyte into the hollow electrode, the lat- 5 ter providing an extended and open overflow lip whereby surplus electrolyte overflows from it in a form exposing a large surface to the atmosphere and is thereby cooled.

ll. In a liquid rheostat, electrodes relatively movable towards and from one another and of similar tapered form respectively internally and externally, and insulatnig proJections on the surface of one of them adapted to make contact with the compleinental surface of the other and thereby limit the approach of the complemental surfaces to one another.

In testimony whereof we affix our signatures.

BERTRAINI GRAY. ROBBINS CURTIS. 

